bald patches

Question
i have a boxer who has got bald patches nearly all over her back   i have been to the vet who have done all  the tests
they have got no answer for it  they are baffled as i am .what can i do next

Answer
It's hard to say without a lot more information - if she's not itching, the vet isn't finding mites, her thyroid is normal (OFA panel), and there are no other skin conditions, it may be something called seasonal flank alopecia - fairly common in Boxers, benign, and generally self-resolving.  Here's a bit more on it:
http://www.dermvet.com/caninesfalopecia.htm

Some people give kelp, melatonin, or canned pumpkin and feel that those help the hair regrow; as far as I know there's not any proof that the hair wouldn't have regrown in the same amount of time without the supplements, but they have other beneficial properties so it wouldn't hurt to try and might at least make you feel like you're doing something. :)

Good luck!